Die holder



Dec. 15, 1936. Q F, BRUCE l y v 2,063,980

DIE HOLDER Filed Sept. 9, 1935 ATTORNEY Patented Dee-1s, "1936` l UNITED STATES nm Houma Chester F. Bruce,l Greeneld, Mass., assignor to Greenfield Tap and Die Corporation, Greenilel d, Mass., a corporation of Massachusetts Application september 9, 1935,'seria1 No'. 39,719

SClaims.

This. invention relates to vholders fordies adapted to cut threads on such articles as screws and rods and the like, and has for its object to obtain greater precision in the use of such'dIeS. 5 'I'he particular type of die holder apparatus to which this invention pertains is that in whicha die is held by a body having a shaft supported l within a driving shank to which the driving force is applied. The driving force is transmitted to l the body by driving surfaces of the shank which c.mate with corresponding surfaces of the body. Owing to` distortion occasionedby heat treatment and desirable manufacturing tolerances,

considerable play has heretofore been allowed to l exist between the body and the shank to enable the mating surfaces to register properly and to permit alignment of the die holder parts on the work.

This play existing, as it does, between the driving shank andlthe shaft of the die holding body has allowed the die to sag somewhat below the driving axis so that the die was not initially centered on the work. In the case of most ordinary` work this sagging is usually of no serious 5 consequence, because upon starting, the die- According to this invention there is provided i for the above type of die holders a device which accurately' centers the die on the work. More specifically, this centering device is a rigid guide which engages a member of the body and a member of the shank in a manner to align the body with .a shank. Preferably the guide is a nut which is threaded on one of the members and has an extension which closely, but slidably, engages the. other member, In a preferred embodiment the guide is a lock nut which threads on the body and locks the die cap, and the extension is a hollow cylinder which receivesy a cylindric member of the shank.

A featm'e of this invention residesin the convertibility provided thereby. vIt is possible, simply by removing the guide o'r replacing'it by an ordinary lock-nut, to cause the holder to revert to the ordinary sagging type. The play which exists in the ordinary sagging holder 'is frequently desirable, to compensate for misalignments in the i5 work.

The invention will be better understood-from the following detailed description of a preferredl embodiment, when considered with theaccompanying drawing, of which Fig. 1 is a sectional view of a die and aholder 5 constructed according to the prior art;

Fig. 2 illustrates a precision type of work which the prior known. apparatus of Fig. 1 is not Well adapted toperform; d'

Fig. 3 is a sectional view of a die and holder .10 constructed according to this invention, adapted to perform the work shown in Fig. 2; and

Fig. 4 is a section taken at line 4-'4 of Fig. 3.

The device of the prior art shown in Fig. 1

comprises a hollow shank I0 having a relatively 15 long cylindrical portion I I terminating in a head portion I2 of larger diameter. A body portion I3 has acylindrical head I4 and a stem I5 which is held within the cylindrical portion I| of the shank. The stem I5 is supported by a restricted 20 portion I6 of the shank and by a collar Il lforced over the end of the stem and held by a screw I8. A spring I9, held in compression between the collar and the restricted portion I6 tends to retain Athe stem within the shank. The body 25 portion is provided with a. pair of parallel at l surfaces 20 and 2| milled, prior to heat treatment, at the region between the head I'4 and the stem I5. These flat surfaces 20 and 2| engage within a pair of corresponding parallel flat driving sur- 30 faces 22 and 23 milled within the head end 'of the shank to form a slot.

The head I4 of the body is centrally hollowed out at- 24, and openings 25-extend through the side of the head to the central opening-24 to`35 permit cuttings to fall away from the holder unit.

The end of the head at 26 forming a ring around the hollow 24 is ground to a nish and provided with lugs 21.

A die 28 abutsthe end 26, and notches 29 in 40 4the base 30 thereof receive the lugs 21. Several lands 3|, having the cutting threads formed on their innersurfaces, extend forward from the base.

A cap 32, having a threaded base 33 and an 45 annular portion 34 held forward by forwardly extending supports between which are -open spaces 35 to permit cuttings to pass, is threaded over the end-of head I4. The annular portion 34 engages the outer surfaces lof the lands so that 5o the ldepth of the cut may be increased when desired by screwing the cap further on the head to compress the lands.` A lock-nut 38 serves to lock the cap in position. j

In operating the unit a torque is ap- 1 at the flats.

plied at the outer cylindrical surface of member II of the driving shank III by any suitable device such as an automatic screw machine. `The flat slot faces 22 and 23 engage the ats 20 and 2| ,y thereby transmitting'the driving torque to the body and the die. Thebody is free to float outwardly, that is, the shaft I5 may withdraw somewhat from the shank against the compression of the spring, so that the die is free to follow its own lead on the work regardless of whatever lag exists in the machine.

In this assembly the head end of the body is carried loosely within the head end of the shank because of the relatively large play at the flats and at the restricted portion I6 of the shank.

There is a closer sliding t at the collar I'I, Vnso the collar acts as a fulcrum from which there occurs a'sag equal to the difference between the true center line A of the shank and the axis of stem I5. The line B indicates the position of the airis vof stem I5 whenit has sagged. The body and stem are shown in Fig. 1 at the true center line, but it should be understood that when the die is not engaged with its work sagging occurs. The play of the stem which permits the sagging exists in all directions; line B indicates the play in the upward direction.

It is not practical to construct the die holder as thus assembled with such small tolerances as to prevent the sagging, largely because of the distortion which commonly occurs during heat treatment, of the individual units. The heat treatment, in the case of the shank, tends to distort the alignment of the head end I2 so that the flat slot surfaces22 and 23 become misaligned and off center with reference to the axis of the shank. Similarly, in the case of the body, the

heat treatment tends' to warp'the head I4 with.

reference to the stem I5 so that the flats 20 and 2| become misaligned and off center with respect to the axis of the stem.

Consequently, if it were attempted to eliminate the sag by reducing the tolerances at the restricted portion I6 and collar I1, a good driving engagement would not be likely to exist at the flats. In spite of the large tolerances provided at the flats the driving engagement would usually be imperfect because only one pair of the mating surfaces would be likely to make contact, owing to the misalignment. A good drivingcon- .tact at both pairs of mating iiat surfaces could be insured only by an expensive grinding operation on the ats subsequent to the heat treatment.

For the above reasons and for reasons Aof manufacturing expediency it has not been found practical to remove the sag or play by removing the play from between the stem and shank; so considerable tolerance is provided at the stem and By reason of these tolerances the die is enabled to center itself on the work even though the heads of the body and shank, including the flats, be somewhat misaligned.

It is noted that the cutting threads are located a considerable distance in front of the nearest bearing at region I6 of the shank; hence, the alignment control of the die is considerably impaired. Furthermore, as the thread cutting proceeds the body shaft is withdrawn somewhat from the shank and the end bearing, or fulcriim, at collar 'II gradually approaches the vbearing at region I8, thus magnifying the substantial initial misalignment.l For the above reasons, the prior known type of holder shown in Fig. 1 must be permitted to sag, which' sagging is usually not serious in the case of ordinary work.

Occasionally, however, thread cutting must be done beyond a projection having a diameter only slightly less than the minor diameter of the screw thread. In such a case, a die, located in a sagging die holder of thel type shown in Fig. 1, would scratch or score the projection in passing over it. In such cases the alignment and iioat must be maintained accurate within very close limits. Fig. 2, whichis an' example of such a case, illustrates a shaft 38. having a projecting end portion 39 of somewhat smaller diameter. The problemis to thread the wider diameter of shaft 38 without scratching the projecting portion 39. The dotted lines indicate the necessary position of one of' the lands 3| of the die in cutting the threads. Obviously, if there is any appreciable sagging of the die holder the protruding portion 39 will be scored.

The more accurate alignment required for this purpose is-provided in accordance with this invention by a die holder of a type like that illustrated in Fig. 3. The assembly of Fig. 3 is nearly the same as that of Fig. 1; and the same numerals in the two gures indicate identical parts. The difference between Figs. 1 and 3 resides in the use, in the unit of Fig. 3, of a combined locknut and extension guide 40, instead of the locknut'36 of Fig. 1. The device 40 comprises a nut portion 4| and a. guide portion 42 having an inner cylindrical surface, and extending back from,

thenut. Holes 43 through the sides of the device 40 register with the side openings 25 of the body head and permit the escape of cuttings.

The inner cylindrical wall of the extension guide is ground with reference to the threads on the nut portion 4I; that is, the longitudinal axes of the threaded part and of the cylindrical extenvsion wall are the same. The outer surface of the cylindrical portion II of the shank is ground with reference to the4 outer cylindrical surface of the head end I2; that is, the axes of these two surfaces are the same. The outer cylindrical surface of the head end I2 may also be ground, if desired, to provide a nice sliding t within the extension guide. Thesegrinding operations are performed after the heat treatment, and very little tolerance is allowed between the engaging surfaces of parts 42 and |2. Hence, since surface 26 of the head is faced with reference to the threads on the head,.the holder unit is accurately aligned from the die to the outer cylindrical surface of part II of the shank.

This new extension guide lock-nut carries the Weight of the die andits carrying parts. It constitutes a bearing around the head of the shank which is closer to the die than the region I6 so that the magnification of the sag is reduced. The use of this aligning device allows work to be threaded closely to a size, concentric and straight. Furthermore, by reason of its use, breakage of dies and spoiled work are reduced.

An important advantage in creating the align- .ment between the body and the shank by means of an outer guide such as 45 resides in the convertibility of the holder unit. It is frequently advantageous to allow some play between the body andto compensate for misalignment of the work. Since such play is present in the holder of Fig. 1 but not in the holder of Fig. 3, it is of considerable advantage to be able to convert a holder according to Fig. 1 into a' holder according to Fig. 3. This conversion is.possible by the selection of a simple lock-nut such as' 36, on the one hand, or an extension guide nut such as 40, on the other hand.

If the rigid alignment of the unit in Fig. 3 were 75 closely, but-slidably, over the outer cylindrical created by a permanent close fitting ofa part within the shank (instead of by a removable part without the shank) the conversion could `not be made.

1l A die holder comprising a hollow driving shank having an enlarged end provided with an outer cylindrical surface,a ,die holding body having a die holding head and a stem which fits loosely within said shank, whereby said body tends to sag below the, longitudinal axis of said shank, means for transmitting driving torque from said shank to said body, and a guide nut threaded over said head, said guide nut having an extension guide provided with an inner cylindrical surface which nts closely, but slldably, over said cylindrical surface of the enlarged end of said shank, thereby preventing said sag of said body.

2. A die holder comprising a hollow driving shank having lan enlarged end provided with an outer cylindrical surface, a die holding body hav- I ing a die holding head provided with an outer Within said shank, whereby the longitudinal axis 0f said body tends to depart from the longitudinal vaxis of said shank, means for transmitting driving torque from said shank to said body, and a guide nut threaded on one of said outer cylindrical surfaces, said guide nut having an extension guide provided with an inner cylindrical surface which ts closely, but slidably,'over the other of said outer cylindrical surfaces, thereby preventing said departure of the axis of said body.

3. A die holder comprising a hollow driving shank having an enlarged end provided with an outer cylindrical surface, a die holding body having a die holding head provided with an outer cylindrical surface and a stem which fits loosely within said shank, whereby said body tends tosag in said shank, means for causing said st'em to move longitudinally ine. the iirction of with drawal from said shank during the thread cutting (operation, means for transmitting driving torque from said shank to said body, and a guid nut threaded on one of said outer cylindrical surfaces, said guide nut having Van extension guide provided with an inner cylindrical surface which fits closely, but slidably, over the other of said' outer cylindrical surfaces, thereby preventing the sag of said body `while permittingthe longitudinal' movement of said stem in said shank.

4. A diel holder comprising a hollow ldriving shank having an enlarged end provided with an -outer cylindrical surface, a die holding body having a die holding head provided with an outer cylindrical surface and a stem which ilts loosely within said shank, a die holding cap threaded on said cylindrical surface `of said head, means for causing said stem to move longitudinally in the direction of withdrawal from said shank during the threadV4 cutting operation, means for transmitting driving torque from said shank to said body, and a nut threaded in back of said cap on said outer cylindrical surface of said head, said nut havinga rearwardly extending guide provided with an inner cylindrical surface which ilts and shank.

surface oi' said enlarged end, said nut acting as a lock nut for said cap and as' aguide which prevents sag of said body.

5. A die holder comprising a shank having a head provided with an outer periphery and a relatively long cylindrical portion having its axis aligned with the'axis of said periphery, a die holding body having ahead provided with a threaded outer periphery and a stem which lits loosely within said shank, means for transmitting driving torque from said shank to said body, and means for aligning the 'axes ofv said body head and of said cylindrical portion, said latter means` comprising a guide nut having an extension guide provided with an inner peripheral surface whose axis is aligned with the axis of the threadsI of said nut, said nut being threaded'o'n said threaded outer periphery and said extension guide tting.

- to be threaded on one of said outer peripheries,

and said guide fitting closely, but slidably, over` the other of said outer peripheries.

7. A die' holder comprising a hollow driving shank having an outer cylindrical area coaxially aligned with a driving portion thereof, a body having inner aligned cylindrical surfaces one of which ts closely over one of said cylindrical areas and another of which fits closely but slidably over the other cylindrical area closely to hold the alignment between said head and driving portion, and yet permit at least some rotary movement between said body and shank.

8. A die holder comprising a hollow shank having a head provided with an outer periphery and a relatively long cylindrical portion having its axis' aligned with the'axis of said periphery,

a die holder body having a head provided with an outer periphery and a stem which fits loosely within said shank, means for transmitting driving torque from said shank.to said body, and a guide y having inner aligned surfaces one of which fits closely over one of said peripheries and the other of which ilts closely but slidably over the other of said peripheries to align the axes of said body head and said cylindrical portion and yet permit atleast some rotary'movemeht between said body cHE's'rFlv E. BRUCE. 

